Mitchel Overdrive, what I learned

sphanna

sphanna

Well-known member
Hi guys and gals,

I just completed installing the Mitchel in my early 30 Fordor. There a couple of things I learned from my experience. If you are installing the sleeve on the short drive shaft that extends forward from the pinion gear, be sure to measure the distance from the banjo face to the center of the hole in the torque tube where you lube the coupling sleeve. This is 17 5/8 inches to center of grease zerk. I did not check this distance and I had to take the unit apart again to move the sleeve about 1/2 inch to enable the grease gun to attach to the zerk. This was quite a frustrating experience for me and it is my hope that if any of you barners are installing a Mitchel, this will save you a lot of work.

I also filled the gear box with the recommended gear lube before I raised the OD unit into position under the car. Do not do this unless you have also installed the speedometer cable extension into the Mitchel first. I lost about 6 ounces if Lube. Add Lube after installation as the directions suggest. Just for information, the unit is filled with exactly 36 fl ozs.

I installed this unit without any help. All alone. I am not an accomplished Model A mech, as many of you on this site are. It can be done but much easier if two people are involved.
 
Congrats on getting it done, especially by yourself! If you have not experienced the Mitchell much before, prepare to be impressed. It is very well made and works flawlessly, and if you drive your A much you will enjoy how effortlessly it cruises and how quiet the car becomes.
 
I did order two pinion wrenches. THe preload on the pinion should be checked and you need 2 wrenches to do this. Also order a new lock washer that goes between the nuts. Do not use the old one. I had to order the pinion puller to remove the pinion. It is a poor quality tool but I made it work. The three bolts supplied only bent the puller. So I drilled and tapped 3 more holes to have 6 bolts to pull the pinion. This worked but still wanted to bend the tool a bit.
 
It is also good to remove the axel from the spring as most seem to think it is safer. Mitchel does not think this is needed. They leave the spring on the axel. If you do as I did, you will need a good quality spring spreader. Our club has one.
 
Steve, good job on doing it yourself and thanks for the info/warnings. I am thinking about getting a Mitchell O/D and don't have too many mechanically inclined friends so installing by myself was one of my concerns. Along with any special tools.

I'm still undecided if I want to go with the O/D or a Mitchell Syncro trans with the higher 1st and 2ndgears. I do mostly in town short jaunts and don't see a need for a O/D.

But neither is happening any time soon so I have time to weigh my options.
 
"I just completed installing the Mitchel in my early 30 Fordor. There a couple of things I learned from my experience. If you are installing the sleeve on the short drive shaft that extends forward from the pinion gear, be sure to measure the distance from the banjo face to the center of the hole in the torque tube where you lube the coupling sleeve. This is 17 5/8 inches to center of grease zerk. I did not check this distance and I had to take the unit apart again to move the sleeve about 1/2 inch to enable the grease gun to attach to the zerk. This was quite a frustrating experience for me and it is my hope that if any of you barners are installing a Mitchel, this will save you a lot of work."


Could you explain in a little more detail about the problem you encountered in your above statement?

I think what you are calling the sleeve is the spline coupler that connects the stub shaft (which I believe you are calling the short drive shaft) to the output shaft up inside the overdrive housing. This spline coupler has the grease fitting in about the middle as I remember. You can install it by inserting either end.

How can it not line up with the window in the aft tube section? You say you moved it by a 1\2 inch. How did you do this?

I have installed a number of Mitchell overdrives and all I did was insert the spline coupler onto the stub shaft and it automatically lined up. What am I not understanding?

Tom Endy
 
sphanna said:
It is also good to remove the axel from the spring as most seem to think it is safer. Mitchel does not think this is needed. They leave the spring on the axel. If you do as I did, you will need a good quality spring spreader. Our club has one.
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You have to understand that the Mitchell Company is in the business of manufacturing overdrives, not installing them. Their installation instructions are probably derived in part from folklore that exits within the Model A hobby. There are many people who remove a rear axle assembly from a Model A with the spring attached and will tell you they have been doing it that way for years without a problem. That does not make it a safe procedure. It only takes one center bolt to break when the rear is out from under the car with the leafs flying 20 feet in the air to make a believer out of you. The rear spring on a Model A Ford is lethal when it is spread and should be approach with caution.

Were I the Mitchell company I would not advise people to remove a rear with the spring attached.

Tom Endy
 
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Y-Blockhead said:
Steve, good job on doing it yourself and thanks for the info/warnings. I am thinking about getting a Mitchell O/D and don't have too many mechanically inclined friends so installing by myself was one of my concerns. Along with any special tools.

I'm still undecided if I want to go with the O/D or a Mitchell Syncro trans with the higher 1st and 2ndgears. I do mostly in town short jaunts and don't see a need for a O/D.

But neither is happening any time soon so I have time to weigh my options.
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The Mitchell overdrive and the Mitchell synchronous transmission are two different things. The overdrive gives you a forth gear above high gear and will also give you a gear between first and second, and second and third. The synchronous transmission gives you a higher first and second if you want, but not a higher high. The advantage of the Mitchell transmission is the ease of shifting and a higher run out in first and second.

I see a great advantage in the overdrive and highly recommend it.

I see by your location you are in the area of the Harbor Area MARC club. If you are not a member I would recommend you join. The installation of a Mitchell overdrive is an easy task for this club. I have assisted them in the past.

Tom Endy
 
sphanna said:
... I had to order the pinion puller to remove the pinion. It is a poor quality tool but I made it work. The three bolts supplied only bent the puller. So I drilled and tapped 3 more holes to have 6 bolts to pull the pinion. This worked but still wanted to bend the tool a bit.
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Did you get the pinion puller from Mitchell? The one I got from them was very robust and worked like a charm. I loaned it to another guy that was installing an OD, and he had nothing but praise for it as well.
 
I also have installed one of these on my own with no dramas, not even misaligning the grease nipple. I left the spring on the axle - a side benefit of which is that it allows you to stand the rear end so that the torque tube is pointing up and it will stay there.
I find however that the unit gets rid of a fair amount of oil through the breather pipe which is mounted as high as it can go - right up under the floor. There is an goo of oil and dirt from the O/D back which I find annoying but other than that, the O/D has transformed the car.
PS I have just completed a 9,000 miles trip towing a camper in this car.
 
Tom. Yes that is exactly what i meant in my post. I put the spline coupler on the stub shaft and it appeared to be correct and it was put on until it came against it's stop at end of splines on stub shaft. I had to remove torque tube from banjo and slide coupler about 1/2 " more from the banjo. I don't know what caused this to be. I called Mitchel and they said this was first they heard of this.
No, I did not get the Mitchel pinion puller. I did not know of that option until after my installation. I purchased my puller from one of the Mod A supplyers. I am very happy with this supplyer's parts and service, but the puller is a little weak if you have a stubbornly stuck 2 face bearing in the banjo.
 
Tom Endy said:
I see by your location you are in the area of the Harbor Area MARC club. If you are not a member I would recommend you join. The installation of a Mitchell overdrive is an easy task for this club. I have assisted them in the past.

Tom Endy
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Thanks Tom. I'll look into the Harbor Area MARC club

Synchro909 said:
I find however that the unit gets rid of a fair amount of oil through the breather pipe which is mounted as high as it can go - right up under the floor. There is an goo of oil and dirt from the O/D back which I find annoying but other than that, the O/D has transformed the car.
Click to expand...

Synchro909, So your saying the O/D unit throws oil out of the breather? Could it have been overfilled? No one else has ever mentioned this.
 
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sphanna said:
Tom. Yes that is exactly what i meant in my post. I put the spline coupler on the stub shaft and it appeared to be correct and it was put on until it came against it's stop at end of splines on stub shaft. I had to remove torque tube from banjo and slide coupler about 1/2 " more from the banjo. I don't know what caused this to be. I called Mitchel and they said this was first they heard of this.
No, I did not get the Mitchel pinion puller. I did not know of that option until after my installation. I purchased my puller from one of the Mod A supplyers. I am very happy with this supplyer's parts and service, but the puller is a little weak if you have a stubbornly stuck 2 face bearing in the banjo.
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I am still trying to understand what caused the problem you encountered. Some pinion pullers I have seen offered by various suppliers is the type where you have to remove the outer large nut on the pinion assembly and then lock the puller in place by reinstalling the nut against it.

If you used this type of puller the pre-load on the double bearing set up was compromised. It may be that the pinion assembly is not properly seated or that there is no pre-load on the bearings.

The Mitchell pinion puller grabs the drive shaft and pushed against the banjo flange and does not disturb those two large nuts which are maintaining the bearing pre-load.

Another possibility is that when the pinion assembly was installed on the Mitchell stub shaft it was not fully seated on the taper. The nut on the end of the stub shaft should have been torqued to a nominal 100 ft lbs.

I don't mean to cause alarm, but if you had to move the spline coupler 1\2" off its seat something is not right and it would be best to determine what caused the problem you saw. Especially if the Mitchell folks were puzzled as well. If the pinion assembly is not as it should be you could have a ring and pinion failure in store.

Tom Endy
 
Tom. The pinion was torqued to 100 f t #'s and the double race bearing was fully seated and flush with the banjo face. The cotter pin was not bent over the end of the shaft, but firmly set towards the shaft. Yes, that was the type of puller i ordered. From Snyder's. I understand what you are saying, but every thing fit perfectly (drive shaft lengths, etc) seems to be working fine.
 
Y Blockhead, I have filled it to the point where oil just starts to run out the filler plug with the car on level ground. The breather pipe always has oil in it at the low point where it has a bit of a sag in it.
 
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